1. Field of the Invention
The present invention relates to an electronic scanning radar apparatus, a receiving wave direction estimating method, and a computer-readable storage media storing a receiving wave direction estimation program. More particularly, the present invention relates to an electronic scanning radar apparatus being preferable to be equipped in a moving body, a receiving wave direction estimating method, and a computer-readable storage media storing a receiving wave direction estimation program, in which the electronic scanning radar apparatus transmits a transmission wave to a target so as to detect the target by receiving a reflection wave of the transmission wave reflected from the target.
Priority is claimed on Japanese Patent Application No. 2010-025950, filed Feb. 8, 2010, the content of which is incorporated herein by reference.
2. Description of the Related Art
All patents, patent applications, patent publications, scientific articles, and the like, which will hereinafter be cited or identified in the present application, will hereby be incorporated by reference in their entirety in order to describe more fully the state of the art to which the present invention pertains.
In general, an electronic scanning radar apparatus is known as radar to be equipped for a moving body. For such radar, a frequency modulated continuous wave (FMCW) radar, multiple-frequency continuous wave radar, pulse radar or the like is employed.
For each radar described above, a receiving wave direction estimating method with array antennas is used for detecting the direction of a receiving wave from a target. The receiving wave may be referred to as an incoming wave, and the target may be referred to as a reflecting object.
Recently, the receiving wave direction estimating method employs highly accurate algorithms such as an auto regressive spectral estimation method (AR spectral estimation method; see FIG. 24), a multiple signal classification method (MUSIC method) or the like, which can provide high resolution (high accuracy) of the direction of receiving waves without increasing channels of receiving antennas. These methods are described in Japanese Unexamined Patent Application, First Publication, Nos. 2006-275840, 2006-47282, 2009-162688 and 2009-156582. These methods are also described in “MATLAB Multi-media Signal Processing part I: Digital signal fundamentals” published by Ikehara and Shimamura in 2004 by BAIFUKAN CO., LTD., and described in “Adaptive Signal Processing with Array Antennas” published by Kikuma in 1998 by Kagaku Shuppan Co. LTD.
The AR spectral estimation method is also referred to as a maximum entropy method (MEM) or a linear prediction method.
For estimating the direction of receiving waves from a target (reflecting object) with those algorithms, input data indicated by complex numbers are converted into a matrix form called as a correlation matrix, and then the estimation process is performed. The input data may be referred to as complex sine wave or sine wave.
These algorithms need to be preset an appropriate number of incoming waves (receiving waves). Even when the algorithms are used for a radar mounted on a moving body, appropriate number of receiving waves are determined. For example, an algorithm such as MUSIC method, which estimates the direction of a receiving wave based on calculations of eigenvalues, needs to calculate eigenvalues of correlation matrixes, so that the algorithm determines the relative size of the calculated eigenvalues and separates the signal components from the noise components. Thereby, the direction of a receiving wave is estimated. See patent publications 2 and 3.
An auto regressive spectral estimation method (AR spectral estimation method) is an algorithm which does not require eigenvalue calculations. The AR spectral estimation method can be under relatively small operation load. The AR spectral estimation method includes an advantage which does not require sensitive settings of the number of receiving waves (the order of model) compared to a multiple signal classification method (MUSIC method).
However, when the number of receiving waves is too small for a setting order of a model, the AR spectral estimation method may occasionally cause an error peak. A final prediction error method (FPE method), an akaike information criterion method (AIC method), a minimum description length method (MDL method), and the like are proposed to estimate the number of receiving waves. However, these methods may not always provide an accurate detecting estimation.
There are rare reports on an estimation method of a number of receiving waves which can be applied to a radar system mounted on a moving body with a small number of channels or objects based on a model with a small number of orders. There are rare technical reports that simplified arithmetic operations provide accurate detections.
The present invention takes into consideration the issues described above. One of the objects of this invention is to provide an electronic scanning radar apparatus, a receiving wave direction estimating method, and a computer-readable storage media storing a receiving wave direction estimation program, which make it possible to accurately detect the direction of receiving (incoming) waves from the target while maintaining the accuracy of the signal detections.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved apparatus and/or method. This invention addresses the need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.